We are planning to continue to study the effect of dibutryl cyclic AMP, theophylline, insulin and ultraviolet radiation on growth and differentiation of chick embryo retinal pigment cells in vitro. The effect of sex hormones and ultraviolet radiation on rodent melanocytes will be studied, including ultrastructural and in vitro studies, using isotopes of dopa and tyrosine as markers for melanogenic activity. Descriptive studies of the pigmentary system of anthropoid apes and other primates have also begun this year, and will be carried out in the coming year, investigating the ultrastructure of the skin of the chimpanzee, gorilla, orangutan and baboon.